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It has been well known for decades that grass can take up and, if cut for silage or hay remove from the field, very large amounts of potash. Typical potash removal values shown in the Nutrient Management Guide (RB209) are equivalent to around 2% K in dry-matter, sometimes higher in fresh grass and lower in […]

Justus von Liebig’s Law of the Minimum states that yield is proportional to the amount of the most limiting nutrient, whichever nutrient it may be (Figure 1). Nitrogen is the nutrient that most frequently provides the largest response, suggesting that this is usually most limiting. However, the plant available potassium status of a soil has […]

Dr Ian Richards, Independent Consultant, Ecopt. Introduction The 13 or so essential nutrients for plants are grouped, in fertiliser regulations, into primary nutrients (nitrogen, phosphate and potash), secondary nutrients (calcium, magnesium, sulphur and sodium) and micronutrients (manganese, copper, boron etc) according roughly to the amounts needed by crops. Don’t be deceived by the term ‘secondary’; […]

Introduction Sulphur is an essential nutrient for all plants, and certain crops are more vulnerable to deficiency than others. Historically, in the UK sulphur was deposited on land from the atmosphere in quantities which were adequate for our crops. However, as the burning of UK coal (high S) in power stations was switched to imported […]

AHDB have just launched their new Nutrient Management Guide (RB209). It is a revision of the Defra Fertiliser Manual (RB209) and it can be viewed or downloaded to your computer from their website www.ahdb.org.uk/rb209. Also, there is an App for mobile devices. Hard copies can be requested by e mail to cereals.publications@ahdb.org.uk. It is supplied free […]

The British Survey of Fertiliser Practice (Defra) shows that since the 1980s rates of Phosphate & Potash fertiliser applications have declined by 1/3 in arable crops, and 2/3 in grassland. With the increase in yields achieved in that time, there is a serious deficit in the P & K being applied from fertilisers, which is […]

With the huge increase in growing forage maize to feed anaerobic digesters, especially in the arable areas of Eastern England, it seems appropriate to consider the harvested offtakes of phosphate and, especially, the high amounts of potash removed.

Soil sampling for the routine measurement of P, K, Mg indices and pH is familiar to most advisers and farmers, with the same well-proven method used for many years. But how are things different where minimum cultivation is practised?

Grass cut regularly, as silage, haylage or hay, removes very large amounts of potassium (K). Unless this is replaced, soil K concentrations will fall. In recent years there is evidence of an overall increase in the number of grassland soils below target index (2-), as well as a decline in the use of potash fertiliser. This situation is not sustainable and grass yields will fall unless corrected.

Having worked out the rate of nutrient potash required for a crop or grass, and considered the timing of the applications, we now have to select a suitable fertiliser product or other source, such as organic manures, to apply to the soil or crop. Then we have to apply it effectively to suit the crop being grown.

As growers and advisers we need to know how much potash we should apply to ensure crops thrive in terms of yield and quality. Previous articles have described the way soils hold potash and how the plants use it. This article takes us on to the reality of deciding how much, and when to apply […]